ODC1 and breast cancer: The key enzymes of polyamine anabolic pathway (Figure 2C), including ornithine decarboxylase 1 (ODC1), spermidine synthase (SRM), and spermine synthase (SMS), had higher expression in the BCSChigh group as compared to the BCSClow group (Figure S2A, Supporting Information), and had higher expression in non‐adherent mammosphere cultures as compared to monolayer cultures in breast cancer cell lines (Figure 2D), suggesting a role of polyamine anabolism in the regulation of the BCSC phenotype.